Measuring Properties of Fast Digitizers Employed for Recording HV Impulses

Requirements on measuring accuracy of high-voltage (HV) impulses employed for testing of self-restoring and non-self-restoring insulation are reviewed in order to select a suitable digitizer for the impulse recording. Certain models of fast digitizers are characterized by an apparently high time resolution, but their actual dynamic performance in case of measuring nonrepetitive, irregularly shaped impluses cannot be deduced from the manufacturer specification. The paper analyzes the "equivalent bits" characteristic which is frequently employed as a criterion of the digitizer dynamic performance, and an additional test of the digitization error distribution is proposed. Such a test results in another characteristic of the "equivalent bits," which is based on the maximum (rather than rms) error and which reflects the actual deformation of the recorded impulse form.